U.S. patent number 5,579,575 [Application Number 08/307,727] was granted by the patent office on 1996-12-03 for method and apparatus for forming an electrical connection.
This patent grant is currently assigned to Raychem S.A.. Invention is credited to Sylvain Briens, Jacques Delalle, Alain Lamome.
United States Patent |
5,579,575 |
Lamome , et al. |
December 3, 1996 |
Method and apparatus for forming an electrical connection
Abstract
A method and apparatus of forming a solder connection between a
plurality of elongate bodies, comprises: (i) forming an initial
connection between the elongate bodies by inserting them into an
induction heatable connecting element of a connector, the connector
comprising a dimensionally heat-recoverable sleeve and, retained
within the sleeve, the connecting element and a solder insert that
is in thermal contact with the connecting element; and (ii) heating
the connector (a) by subjecting the connecting element to an
alternating magnetic field so that it is heated by induction
thereby melting the solder insert, and (b) subjecting the sleeve to
hot air and/or infrared radiation, thereby causing the sleeve to
recover. The apparatus for applying heat to an elongate connector,
comprises a first heat source which comprises an induction coil,
and a second heat source arranged to generate hot air or infrared
radiation.
Inventors: |
Lamome; Alain (Pierrelaye,
FR), Delalle; Jacques (Triel sur Seine,
FR), Briens; Sylvain (Soisy Sous Montmorency,
FR) |
Assignee: |
Raychem S.A.
(FR)
|
Family
ID: |
10713284 |
Appl.
No.: |
08/307,727 |
Filed: |
September 23, 1994 |
PCT
Filed: |
March 30, 1993 |
PCT No.: |
PCT/GB93/00658 |
371
Date: |
September 23, 1994 |
102(e)
Date: |
September 23, 1994 |
PCT
Pub. No.: |
WO93/20596 |
PCT
Pub. Date: |
October 14, 1993 |
Foreign Application Priority Data
Current U.S.
Class: |
29/860; 174/88C;
174/DIG.8; 219/476; 219/605; 228/227; 29/872 |
Current CPC
Class: |
H01R
4/723 (20130101); H01R 43/0242 (20130101); H01R
9/0503 (20130101); H01R 9/0512 (20130101); Y10T
29/49179 (20150115); Y10T 29/49201 (20150115); Y10S
174/08 (20130101) |
Current International
Class: |
H01R
43/02 (20060101); H01R 4/72 (20060101); H01R
4/70 (20060101); H01R 9/05 (20060101); H01R
043/02 (); H05B 003/02 () |
Field of
Search: |
;29/872,860
;174/88C,DIG.8 ;264/230 ;228/227 ;219/476,605 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0159945 |
|
Oct 1985 |
|
EP |
|
0371458 |
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Jun 1990 |
|
EP |
|
0371455 |
|
Jun 1990 |
|
EP |
|
0405561 |
|
Jan 1991 |
|
EP |
|
0420480 |
|
Apr 1991 |
|
EP |
|
57-45025 |
|
Mar 1982 |
|
JP |
|
4-247930 |
|
Sep 1992 |
|
JP |
|
WO90/03090 |
|
Mar 1990 |
|
WO |
|
WO92/00616 |
|
Jan 1992 |
|
WO |
|
Primary Examiner: Arbes; Carl J.
Attorney, Agent or Firm: Burkard; Herbert G. Novack; Sheri
M.
Claims
We claim:
1. A method of forming a solder connection between a plurality of
elongate bodies, which comprises:
(i) forming an initial connection between the elongate bodies by
inserting them into an induction heatable connecting element of a
connector, the connector comprising a dimensionally
heat-recoverable sleeve and, retained within the sleeve, the
connecting element and a solder insert that is in thermal contact
with the connecting element; and
(ii) heating the connector (a) by subjecting the connecting element
to an alternating magnetic field so that it is heated by induction
thereby melting the solder insert, and (b) simultaneously
subjecting the sleeve to at least one of hot air and infrared
radiation, thereby causing the sleeve to recover.
2. A method as claimed in claim 1, wherein the hot air and/or
infrared radiation is applied to a portion of the sleeve which is
longitudinally spaced apart from a portion of the sleeve which
retains the connecting element.
3. A method as claimed in claim 1, wherein the infrared radiation
is applied to the sleeve by means of a heating element located
outside the sleeve, which element is heated by induction.
4. A method as claimed in claim 3, wherein the alternating magnetic
field that heats the connecting element is produced by an induction
coil which also heats the heating element.
5. A method as claimed in claim 1, wherein the connecting element
has an internal screw thread and the initial connection between the
elongate bodies is formed by screwing the bodies into the
connecting element so that they are held therein.
6. A method of forming a solder connection between a plurality of
elongate bodies, which comprise:
(i) forming an initial connection between the elongate bodies by
inserting them into an induction heatable connecting element of a
connector, the connector comprising a dimensionally
heat-recoverable polymeric sleeve and, retained within a
longitudinal portion only of the sleeve, the connecting element and
a solder insert that is in thermal contact with the connecting
element; and
(ii) heating the connector (a) by subjecting said longitudinal
portion of the sleeve enclosing the connecting element to an
alternating magnetic field so that the connecting element is heated
by induction thereby melting the solder insert, and (b)
simultaneously subjecting the sleeve beyond said longitudinal
portion to at least one of hot air and infrared radiation, thereby
causing the sleeve to recover.
7. An apparatus for applying heat to an elongate connector,
comprising:
(i) a first heat source comprising an induction coil arranged to
generate an alternating magnetic field, and
(ii) a second heat source arranged to generate infrared radiation,
wherein
(iii) the first source is disposed around a first portion of the
connector that encompasses an induction heatable connecting
element, and wherein
(iv) the second source comprises a hollow rigid component that is
arranged to surround a second portion of the connector that
encompasses a dimensionally heat-recoverable polymeric sleeve and
that is longitudinally spaced apart from said first portion of the
connector.
8. An apparatus as claimed in claim 7, wherein the second heat
source is arranged to be heated by the first heat source.
Description
This invention relates to the formation of connections between
elongate bodies, particularly electrical connections and especially
connections between electrical wires and cables.
In many instances it is desired to form a solder connection between
two or more wires. This can, for example be achieved by means of
solder connection devices comprising a small dimensionally
heat-recoverable sleeve which contains a quantity of solder. The
wires can be inserted into the sleeve after the ends have been
stripped of insulation, and the device can then be heated, for
example by means of a hot-air gun or by an infrared lamp, to
recover the sleeve about the wires and to melt the solder inside
the sleeve. A device for forming such a solder connection is
disclosed in International Patent application publication No.
WO92/00616, the disclosure of which is incorporated herein by
reference. That device comprises a metallic connecting element in
the form of a tapering helical coil of wire located in a
dimensionally heat-recoverably sleeve, and a quantity of solder.
The device enables a temporary or initial electrical connection to
be formed by screwing the device onto the wires and then, for
example after the connection has been electrically tested, the
device can be heated to form a permanent electrical connection. By
means of such devices it is possible to form very reliable solder
joints which are sealed against ingress of moisture. However in
many cases a degree of skill is required on the part of the
operator in order to ensure that the solder is fully melted but at
the same time to prevent overheating of the wire insulation the
heat-recoverable sleeve or the like.
Self-regulating induction heating has been used in an attempt to
prevent overheating. For example, European patent application,
publication No. 0371458 discloses a method of terminating an
electrical wire at a connector assembly, in which the connector
terminal, comprising a solder tail, has a thin layer of a
self-regulating heating source bonded to it. The self-regulating
heating source comprises a foil having a first layer of copper or
copper alloy which has a low resistance and minimal magnetic
permeability, and a second thin layer of magnetic material such as
nickel-iron alloy. The electrical wire is terminated by placing a
stripped end of the wire over the solder tail. An alternating
magnetic field is then applied to the self-regulating heating
source, at a frequency of 13.56 MHz for example, causing the solder
tail to heat up and melt the solder and cause the sleeve to shrink.
Because the heating source is self-regulating, it may be heated to
a pre-selected maximum temperature sufficient to melt the solder
and shrink the sleeve.
European patent application No. 0420480 discloses an alternative
method of terminating an electrical wire at a connector assembly,
wherein a self-regulating induction heater preform comprising a
band of bipartite metal having a first layer of non-magnetic metal,
e.g. copper, and a second layer of high magnetic permeability
metal, e.g. an alloy of nickel and iron, is crimped around a
stripped end of the wire to be terminated. A heat-recoverable
sleeve containing a solder preform is then installed on a connector
terminal and the stripped end of the wire which has the band of
bipartite metal crimped on it is inserted into the sleeve. The
bipartite metal band is then heated by induction by placing an
inductance coil around the sleeve and applying a high frequency
alternating current, e.g. 13.56 MHz in the coil. The heating of the
bipartite metal band causes the solder preform to melt and the
sleeve to recover. Optionally, a preliminary assembly step may be
carried out, whereby the heat-recoverable sleeve is pre-installed
on the connector terminal by applying a limited amount of heat to a
leading end of the sleeve to cause the leading end to recover about
part of the terminal.
A further method of using self-regulating induction heating to form
a soldered electrical connection is disclosed in European patent
application, publication No. 0405561. In this method, the
self-regulating induction heater comprises a preform that is either
wrapped around or against a solder preform within a length of
heat-recoverable tubing. The heater preform is formed from a first
layer of copper or copper alloy having a thickness of for example
0.05 mm and a second layer of magnetic material such as nickel-iron
alloy having a thickness of 0.01 mm to 0.015 mm for example. The
preform is formed as a thin layer and preferably has a spiral shape
so that it is easily reduceable in diameter to permit the sleeve of
heat-recoverable tubing to reduce in diameter upon being heated to
its recovery temperature.
European patent application, publication No 0371455 discloses a
different approach to self-regulating induction heating. In this
approach, a heat-recoverable sleeve containing a solder preform is
heated by means of a self-regulating heater strap which is wrapped
around the sleeve. The strap comprises a first layer of copper or
copper alloy having a thickness of for example 0.05 mm and a second
layer of magnetic material such as nickel-iron alloy having a
thickness of for example 0.01 mm to 0.015 mm. The strap is heated
either by induction or by direct application of an alternating
current, and the heat generated in the strap melts the solder
preform and causes the sleeve to recover. This approach may
sometimes be used to seal solder tails of the type disclosed in
EP0371458 when the tails are not used to terminate an electrical
wire. In this case, the strap may be used to heat and shrink an end
region of the sleeve which is not located around the solder tail
and the solder tail may be heated by induction in order to heat and
shrink the part of the sleeve that is located over the solder
tail.
The use of induction, however, as a means of heating solder
connection devices has a problem in that the degree to which the
various components of the device are heated depends on the nature
of the components themselves as well as the induction heating
source. For example the frequency of the power source that is
needed in order to raise the elongate bodies, e.g. copper wires, to
the required temperature is not the same as that needed to melt the
solder or to recover the sleeve. This can be seen by considering
the skin depth which is given by the relationship ##EQU1## where
.delta. is the skin depth measured in metres, .rho. is the
resistivity of the component considered, .mu. is its relative
magnetic permeability and .mu. is the frequency of the ac field of
the work coil. Thus, as the resistivity and magnetic permeability
of the various components differ, the skin depth will differ and
will not normally match the physical thickness of the
components.
According to one aspect of the present invention, there is provided
a method of forming a solder connection between a plurality of
elongate bodies, which comprises:
(i) forming an initial connection between the elongate bodies by
inserting them into an induction heatable connecting element of a
connector, the connector comprising a dimensionally
heat-recoverable sleeve and, retained within the sleeve, the
connecting element and a solder insert that is in thermal contact
with the connecting element; and
(ii) heating the connector (a) by subjecting the connecting element
to an alternating magnetic field so that it is heated by induction,
thereby melting the solder insert, and (b) subjecting the sleeve
hot air and/or infrared radiation, thereby causing the sleeve to
recover.
According to another aspect of the invention, there is provided an
apparatus for applying heat to an elongate connector,
comprising
(i) a first heat source comprising an induction coil arranged to
generate an alternating magnetic field, and
(ii) a second heat source arranged to generate hot air or infrared
radiation, wherein
(iii) the first source is disposed around a first portion of the
connector, and wherein
(iv) the second source comprises a hollow rigid component that is
arranged to surround a second portion of the connector that is
longitudinally spaced apart from said first portion of the
connector.
The method and apparatus according to the present invention have
the advantage that it is possible for the heat-recoverable sleeve
and other components of the connector with greatly differing
physical and electrical properties to be heated by the correct
amount during formation of the connection. A problem associated
with previous methods and apparatus for forming solder connections
is that one or more of the different components of the connector
are normally overheated in order to ensure that another of the
components is heated sufficiently. For example, if only an external
source of heating, e.g. hot air or infrared radiation, is used both
to recover the heat-recoverable sleeve and to melt the solder, the
recoverable sleeve will overheated because all of the heat required
to melt the solder needs to pass through the sleeve. Overheating
may, for example, degrade the properties of the sleeve and is in
any case inefficient and time-consuming. Alternatively, however, if
only an internal source of heating, e.g. by induction, is used the
solder may be overheated because the thermal conduction from an
internal heating element to the solder is much more rapid than
conduction from the heating element to the extremities of the
heat-recoverable sleeve or from the heating element along the
elongate bodies, e.g. wires and through the wire insulation, to the
extremities of the heat-recoverable sleeve. Overheating of the
solder may cause the solder to `wick` along the wires or `squirt`
out of the connector, thereby causing short circuits or `dry`
connections. In addition, overheating of the solder may cause
overheating of the sleeve in the vicinity of the solder, and in any
case is inefficient and time-consuming.
The present invention solves, or at least alleviates, the above
problems associated with previous methods and apparatus, since it
normally enables the correct amount of heat to be supplied to the
solder in order to melt it and the correct amount of heat to be
supplied to the sleeve in order to cause it to recover,
substantially without overheating any component of the connector
or, for example, the insulation of wires connected by means of the
connector.
According to a preferred embodiment of the invention, the connector
is heated by both the hot air and/or infrared radiation
substantially simultaneously. This has an advantage in that not
only is overheating of components of the connector normally
avoided, but also the time taken to melt the solder and recover the
sleeve can normally be reduced significantly in comparison to
conventional methods, due to the two sources of heat complementing
each other.
The present invention is especially advantageous for forming a
solder connection by means of a connector which has part of its
dimensionally heat-recoverable sleeve extending beyond at least one
end of the connecting element. In this case, heating the connector
solely by induction can be inefficient and time-consuming since the
further the sleeve extends away from the connecting element, the
less efficient and more time-consuming is the transfer of heat from
the connecting element to the end of the sleeve. Hence, according
to a preferred aspect of the invention, the hot air and/or infrared
radiation is applied to a portion of the sleeve which is
longitudinally spaced apart from a portion of the sleeve which
retains the connecting element, which is heated by induction.
The connecting element of the connector which is used to form the
solder connection may be formed from substantially non-magnetic
material, for example copper and particularly hard temper copper.
Preferably, however, the connecting element is formed from high
magnetic permeability material. The phrase "high magnetic
permeability material" is intended to mean a material having a
relative magnetic permeability, at low H fields, of at least 5,
more preferably at least 10 and especially at least 100, but will
often be 1000 or more. The connecting element is normally hollow
and open-ended so that the ends of the bodies can be inserted
therein, and preferably has a screw-threaded interior so that they
can be screwed into it and will then be temporarily held therein.
The connecting element may be made in a number of ways and from a
number of materials. The heat may be generated in the element by
hysteresis losses or by eddy current losses or by both mechanisms
depending on the material from which the element is formed. For
example the element may be formed from a conductive, substantially
non-magnetic material such as copper, or a ferromagnetic material
such as low carbon steel, in which case the heating effect will be
caused by eddy current losses, or it may be formed from a
ferrimagnetic material such as a ferrite in which case the heating
effect will be due to hysteresis losses.
The connecting element can be made from a wire by coiling it up,
normally into a frusto-conical configuration so that the wire
itself provides the screw thread on the interior of the element. In
this case the wire forming the element may be provided with a pair
of flat faces extending along its length that join to form a ridge,
for example it may have a polygonal cross-section, to make the
screw thread more pronounced. Such an element would have a form
generally as shown in international patent application No.
WO/9200616. This form of element, as can others, may be formed from
materials such as copper or steel, especially low carbon steel, or
from ferritic stainless steel. Alternatively, the element may be
formed from a solid block, for example a machined block or formed
by other methods, in which case it may be formed from a metal as
described above or from a non-metallic high permeability material
such as a sintered ferrite, especially one having a Curie
temperature in the range of from 225.degree. to 250.degree. C. Such
a material has the advantage that it enables the heating method to
heat the article to a temperature in the region of the Curie
temperature, so causing the solder to melt (eg. an Sn.sub.63
Pb.sub.37 eutectic will have a melting point of 183.degree. C.) but
the heating efficiency will fall off rapidly at temperatures above
the Curie point of the element and thereby limit the temperature
rise of the article to one governed by the Curie point of the
element. If it is desired to improve the degree of control over the
heating step, it is often possible to monitor the reduction of the
magnetic field strength in the region of the connecting element as
the element passes through its Curie temperature and to use this
reduction to control the termination of the heating step, eg. by
stopping power to the heating coil.
According to the invention the recoverable sleeve will recover, and
any sealant will fuse, principally due to the effect of the hot air
and/or infrared radiation, whereas the copper conductors to be
connected will be heated almost entirely by thermal conduction from
the connecting element. In most instances the solder will be heated
principally by thermal conduction from the connecting element
although a significant amount of heating of the solder may occur
due to the hot air or infrared heater. Where the connecting element
is in the form of a coil, the solder will flow through the windings
of the coil into its interior and so connect the conductors with
the element, and if the element is formed from a solid block of
material, it will be necessary to form a number of holes in the
element to allow the solder access to the interior of the
element.
As stated above the sleeve is dimensionally heat-recoverable, that
is to say the article has a dimensional configuration that may be
made substantially to change when subjected to heat treatment.
Usually these articles recover, on heating, towards an original
shape from which they have previously been deformed but the term
"heat-recoverable", as used herein, also includes an article which,
on heating, adopts a new configuration, even if it has not been
previously deformed.
In their most common form, such articles comprise a heat-shrinkable
sleeve made from a polymeric material exhibiting the property of
elastic or plastic memory as described, for example, in U.S. Pat.
Nos. 2,027,962; 3,086,242 and 3,597,372. As is made clear in, for
example, U.S. Pat. No. 2,027,962, the original dimensionally
heat-stable form may be a transient form in a continuous process in
which, for example, an extruded tube is expanded, whilst hot, to a
dimensionally heat-unstable form but, in other applications, a
preformed dimensionally heat-stable article is deformed to a
dimensionally heat-unstable form in a separate state.
In the production of heat-recoverable articles, the polymeric
material may be cross-linked at any stage in the production of the
article that will enhance the desired dimensional recoverability.
One manner of producing a heat-recoverable article comprises
shaping the polymeric material into the desired heat-stable form,
subsequently cross-linking the polymeric material, heating the
article to a temperature above the crystalline melting point or,
for amorphous materials the softening point, as the case may be, of
the polymer, deforming the article and cooling the article whilst
in the deformed state so that the deformed state of the article is
retained. In use, since the deformed state of the article is
heat-unstable, application of heat will cause the article to assume
its original heat-stable shape.
Any material to which the property of dimensional recoverability
may be imparted may be used to form the sleeve. Preferred materials
include low, medium or high density polyethylene, ethylene
copolymers, eg. with alpha olefins such as 1-butene or 1-hexene, or
vinyl acetate, polyamides or fluoropolymers, eg.
polytetrafluoroethylene, polyvinylidine fluoride or
ethylene-tetrafluoroethylene copolymer.
The solder employed in the connector is a soft solder as distinct
from brazing material. The solder may, for example, simply be in
the form of an Sn.sub.63 Pb.sub.37 eutectic composition which will
melt as the device is heated and the sleeve recovers, or more than
one solder composition having differing melting points may be
employed, as described in International Application No. WO88/09068.
In this form of device, melting of the higher melting point
component, eg. Sn.sub.96.5 A.sub.g3.5 eutectic will provide a
visual indication that the device has been heated sufficiently to
melt the lower melting point composition and to form a satisfactory
solder joint. If desired the lower melting point solder may be a
non-eutectic composition and, for example as described in
International Application No. WO90/09255, the higher and lower
melting point solder compositions may together form a eutectic
composition. For example, a non-eutectic Sn.sub.60 Pb.sub.40 lower
melting point component may be employed with a higher melting point
component formed from pure tin in relative amounts that an
Sn.sub.63 Pb.sub.37 eutectic is formed. The disclosures of these
two patent applications are incorporated herein by reference. An
advantage of employing a two component solder, and especially a
tin, Sn.sub.60 Pb.sub.40 combination is that it reduces the
possibility of "wicking" that is to say, travel of the solder along
the conductors and away from the joint area due to capillary action
by the stranded conductors, which can be caused by prolonged
heating of the device.
The solder may be positioned anywhere where it will be able to flow
into the connecting element to form a solder joint and where it is
in good thermal contact with the element. The solder may be
employed in the form of a ring or in any other form for example a
ball, and may be disposed symmetrically about the sleeve axis or
offset from it. The solder element may, for instance, be located at
the smaller diameter end of a frusto-conical connecting element in
which case it may be in the form of a ball or plug, or it may be
located in the region of a large diameter end of the connecting
element, for example in the form of a ring. Preferably the solder
is in the from an element that surrounds the connecting element,
especially where the connecting element is in the form of a coil so
that the fused solder can flow through the windings of the coil to
the interior thereof. More than one quantity of solder may be
employed, for example where the connecting element has more than
one tapering internal surface for forming a splice.
The hot air and/or infrared heating step may be carried out before
or after the induction heating step or simultaneously therewith. If
the two heating steps are carried out simultaneously the hot air
gun or infrared lamp may be incorporated into the induction heating
coil.
The infrared heating source may be provided by a hollow rigid
component which can be excited by an induction coil if chosen of
suitable material. It may be convenient to use a single source of
induction heating by combining the induction coil of the infrared
heating source with a coil that is used to heat the connecting
element. In this arrangement the entire heating of the connector
and the connection may be carried out substantially
simultaneously.
As mentioned above, the second heat source of the apparatus
according to the invention comprises a hollow rigid component.
According to a preferred embodiment of the apparatus according to
the invention, the second heat source is arranged to be heated by
induction, and once heated, to generate infrared radiation. It is
particularly preferred that the second heat source is arranged to
be heated by the first heat source. This has the advantage that
only one source of power is needed to heat an article both by
induction and by infrared radiation.
Depending on the particular requirements and the composition of the
connector, the hollow rigid component may be formed from any of a
variety of different materials and may have any of a number of
different forms. For example, for certain applications the
component may be formed from a material of high magnetic
permeability, e.g. a ferrite or low carbon steel, but for other
applications, the element may be formed from substantially
non-magnetic material, e.g. copper. The choice of material which
best suits the particular requirements will normally be made on a
trial and error basis. Also depending on the particular
requirements, the component may, for example, have a substantially
cylindrical or conical shape, or it may comprise at least one
coil.
In addition to the method and apparatus, the present invention also
provides a solder connection between a plurality of elongate bodies
that has been formed by the method according to the invention.
The method and apparatus according to the present invention will
now be described by way of example with reference to the
accompanying drawings in which:
FIG. 1 is a side sectional elevation of a connector that is
employed in the present invention;
FIG. 2 is a side section view of the connector of FIG. 1 together
with wires during the heating step;
FIG. 3 is a side sectional elevation of a second form of
connector;
FIGS. 4 and 5 are partially cut-away views of alternative forms of
connecting element; and
FIGS. 6 and 7 are schematic representations of one form of
apparatus according to the invention, showing a connector being
inserted into the apparatus and heated.
Referring to the accompanying drawings, FIG. 1 shows a connector
for forming a solder joint between a number of electrical wires 2
which comprises a dimensionally heat-recoverable sleeve 3 formed
from crosslinked and expanded polyvinylidine fluoride, and a
connecting element 4 formed as a frusto-conical spring or coil of
low carbon steel wire. The steel wire can have a cross-section for
example in the form of a square or a rhombus in which sides,
forming faces on the wire, are arranged at an angle of
approximately 60.degree. to one adjacent side and at an angle of
approximately 120.degree. to the other adjacent side. The wire is
coiled up so that the ridges formed by the faces that are at
60.degree. to each other are located on the interior and the
exterior of the element, the interior ridge forming a screw thread
for holding the wires to be connected. One end of the wire located
at the smaller diameter end of the connecting element 4 is bent so
that it extends across the axis of the coil and prevents over
insertion of the conductors to be connected. In some instances it
may be advantageous to expand the diameter of the coil 4 by opening
out the ends of the copper wire 5 and retaining them in their new
position.
A ring 8 of Sn.sub.63 Pb.sub.37 eutectic solder is located about
the external surface of the connecting element 4 between the
connecting element and the heat-shrinkable sleeve 3. As shown, the
solder ring is relatively thick and short, its axial length being
only approximately twice its radial thickness, although in many
instances it may be desirable for the ring to be thinner and longer
in order to improve the thermal contact with the connecting
element.
One end of the sleeve in the region of the smaller diameter end of
the connecting element is pre-recovered onto a spherical sealing
element 10 formed from a fusible polymeric material, eg.
polyethylene, and a further sealing element 11 in the form of a
ring is located within the sleeve adjacent to the other end of the
connecting element 4.
In order to form an electrical connection between the wires 2 in a
bundle, their ends are stripped of insulation and inserted into the
open end of the connector 1 until they abut the end of the end of
the wire 5 that has been bent across the axis of the coil and acts
as a stop. The connector 1 is then given a small twist to screw the
wires 2 into the connecting element 4 and hold the connector on the
wires. The wires and connector are then both inserted into an
induction heating coil 12 which is powered up. During this process
the connecting element heats up and causes the solder ring 8 to
melt and flow through the windings of the coil to its interior and
so form a solder bond between the wires and the connecting
element.
Simultaneously with the induction heating step, the device is
briefly heated externally with hot air by means of a hot air gun
13. The temperature, flow rate and heating cycle time of the hot
air gun is set so that the hot air will not, on its own, melt the
solder ring 8, but it will cause the heat-recoverable sleeve 3 to
shrink about the wires and the sealing ring 11 to melt. A stub
splice that is sealed against moisture ingress is thereby
formed.
FIG. 3 shows a form of connector according to the invention of the
form described in International patent application No.
PCT/GB92/02257 for connecting one or more ground leads to the
shield of a coaxial cable. This form of connector comprises a
heat-recoverable polyvinylidine fluoride sleeve 31 that contains a
generally diabolo shaped connecting element 32 wraps of fluxed
Sn.sub.63 Pb.sub.37 eutectic solder 33' and 33", and a pair of
fusible polyethylene sealing rings 34' and 34", one sealing ring
being located at each end of the connecting element 32. As
described above, the connecting element has been formed from by
coiling a low carbon steel wire that has a square
cross-section.
In use a central portion of the outer jacket 35 of a coaxial cable
36 is removed in order to expose a portion of the braid 37 forming
the screen. One or more ground leads 38 can be inserted into one
open end of the connecting element 32 and the element 32 can then
be twisted about the coaxial cable 36 and the ground lead in order
to grip the ground lead. The connector can be heated by means of an
induction coil and hot-air gun as described in FIGS. 1 and 2 to
form a sealed splice.
The connecting element 32 is capable of expanding at its waist if
necessary in order to fit over coaxial cables of a range of
diameters, the maximum diameter being determined by the size of the
chamber formed by the central section 38 of heat-recoverable sleeve
31. Provision of the solder 33 in the form of wrap will allow the
solder to accommodate any increase in size of the connecting
element.
FIGS. 4 and 5 show two further connecting elements and solder rings
that may be employed in connectors used in the present invention.
This form of element 40, frusto-conical as shown in FIG. 4 and
diabolo as shown in FIG. 5 are formed from a sintered ferrite, eg.
a Mn Ni or Ni Zn ferrite having a Curie point between 200.degree.
and 250.degree. C. The elements 40 are formed by moulding or
machining solid bodies of the ferrite. Usually it will be necessary
for holes 41 to be provided in the elements in order to enable the
solder 42 to flow into the interior of the element after fusing.
The elements 40 may be provided with teeth or a screw thread 43 on
their interior surface in order to allow the elements to grip the
stripped wire ends that are to be connected by a simple twisting
action as described above. These forms of connecting elements may
be employed in connectors as shown in FIGS. 1 and 3 exactly as
described above with the exception that the rate at which the
elements 40 will generate heat will fall considerably as the
element passes through its Curie temperature, so that the risk of
overheating in the induction heating step is reduced.
FIG. 6 is a schematic representation of the connector 1 prior to
being inserted into a hollow rigid component 52 and induction coils
51' and 51" of heating apparatus 50. The induction coils 51' and
51" may comprise separate coils or they may be parts of a single
coil. The component 52 comprises a substantially cylindrical
component located inside the induction coil 51'.
FIG. 7 shows the connector 1 disposed in the apparatus 50 and after
the connection has been made. To achieve this an alternating
current has been passed through the induction coils 51' and 51",
which has generated an alternating magnetic field inside the coil.
The alternating magnetic field heated the connecting element 4 in a
first heating zone A by induction in the coil 51", and thermal
conduction from the connecting element has melted a solder ring 8
(shown in FIG. 1). The alternating magnetic field generated by the
coil 51' has heated the hollow rigid component 52 by induction in a
second heating zone B, which has caused the component to radiate
infrared radiation, thereby heating the heat-recoverable sleeve 3
in the zone B and causing it to recover about the wires 2.
* * * * *